Particular difficulty has been found in the present method of smoke spot testing the smoke content in the flue pipe of an oil burner, and in determing the Smoke Spot Number. Namely, the filter paper in common use today is in strip form and is obtained by the technician tearing off a useable piece of paper from a serrated sheet to form a useable strip. Herein lies one of the difficulties. Usually the technician making the test has either serviced the oil burner or has made an inspection. As a result his hands are quite often covered by a quantity of soot, oil, dust, or other matter generally found around an oil burner. Hence, the moment he selects a filter strip he imparts a print or smudge from his hands onto the filter paper even before he makes a test. This contamination can degrade the test data and lead to an erroneous conclusion. Also, the concept of placing a small strip of limp paper in a narrow slot is awkward and difficult and often falls out of the tester and on the floor where it is further dirtied.
Another difficulty of importance is that after a smoke spot test has been made, the test strip of filter paper must be removed from the spot tester and physically placed next to a standard smoke scale for inspection. In so doing, the test paper has to be handled again and can be easily smudged or dropped, further contamination resulting. Since several tests are usually made on one strip, any disorientation of the test strip by being dropped can cause confusion as to which was the first or the last test.